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| United States Patent |
5,512,798
|
|
Honda
|
April 30, 1996
|
Low-pressure mercury vapor discharge lamp and illuminating apparatus
utilizing same
Abstract
A low-pressure mercury vapor discharge lamp includes a light-transmitting
tube containing discharge medium, a pair of discharge electrodes each
mounted in a vicinity of respective end portions of the tube, a
transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, and the transparent conductive film
having a thickness on one end portion of the tube relatively thinner than
a thickness of the transparent conductive film on the other end portion of
the tube. A phosphor film is coated on an inside surface of the
transparent conductive film on an inside surface of the tube. The
discharge lamp has a feature reduced in blackening on the transparent
conductive film. A portion more capable of decreasing ultraviolet causing
electrical resistance to change, such as the thick portion of the phosphor
film and/or an ultraviolet decreasing film, is coated to the inside
surface of the conductive film where the stability of the resistance
relatively low, specifically the thick portion of conductive film in which
more undecomposed material remains. The change in the resistance of the
conductive film is balanced between both ends of the lamp bulb.
| Inventors:
|
Honda; Hisashi (Yokosuka, JP)
|
| Assignee:
|
Toshiba Lighting & Technology Corporation (Tokyo, JP)
|
| Appl. No.:
|
317590 |
| Filed:
|
September 30, 1994 |
Foreign Application Priority Data
| Sep 30, 1993[JP] | 5-244897 |
| Mar 31, 1994[JP] | 6-062309 |
| Mar 31, 1994[JP] | 6-064022 |
| Current U.S. Class: |
313/489; 313/483; 313/485; 313/635 |
| Intern'l Class: |
HO1J 001/62; HO1J 017/16 |
| Field of Search: |
313/489,483,485,635
|
References Cited
U.S. Patent Documents
| 5227693 | Jul., 1993 | Sakakibara | 313/489.
|
| 5258689 | Nov., 1993 | Jansma | 313/489.
|
| Foreign Patent Documents |
| 0001057 | Jan., 1980 | JP.
| |
| 0133652 | Dec., 1983 | JP.
| |
| 0018560 | Jan., 1984 | JP.
| |
| 0298639 | Dec., 1989 | JP.
| |
| 0294245 | Apr., 1990 | JP.
| |
Primary Examiner: O'Shea; Sandra L.
Assistant Examiner: Ning; John
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt
Claims
What is claimed is:
1. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing a discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, said transparent conductive film having
a thickness at one end portion of the tube thinner than a thickness of the
transparent conductive film at the other end portion of the tube; and
a phosphor film coated on the transparent conductive film, said phosphor
film having a thickness at said one end portion of the tube thinner than a
thickness of the phosphor film at said other end portion of the tube.
2. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing a discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, said transparent conductive film having
a thickness at one end portion of the tube thinner than a thickness of the
transparent conductive film at the other end portion of the tube;
an ultraviolet decreasing film coated on the transparent conductive film;
and
a phosphor film coated on the ultraviolet decreasing film, wherein a
combined thickness of the ultraviolet decreasing film and the phosphor
film at said one end portion of the tube is thinner than a combined
thickness of the ultraviolet decreasing film and the phosphor film at said
other end portion of the tube.
3. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing a discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof with a small quantity of an additive and coated on an inner
surface of the light-transmitting tube between the discharge electrodes,
wherein a content of the additive in the transparent conductive film at
one end portion of the tube is greater than a content of the additive in
the transparent conductive film at the other end portion of the tube; and
a phosphor film coated on the transparent conductive film, said phosphor
film having a thickness at said one end portion of the tube thinner than a
thickness of the phosphor film at said other end portion not the tube.
4. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing a discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on the inner surface of the light-transmitting tube
between the discharge electrodes, wherein said transparent conductive film
has a thickness at one end portion of the tube thinner than a thickness of
the transparent conductive film at the other end portion of the tube and
has a thickness at a middle portion of the tube thicker than the
thicknesses of the transparent conductive film at either end portion of
the tube; and
a phosphor film coated on the transparent conductive film, wherein the
phosphor film has a thickness at said one end portion of the tube thinner
than a thickness at said other end portion of the tube and has a thickness
gradually increasing from said one end portion to said other end portion
of the tube.
5. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film coated on an inner surface of the
light-transmitting tube between the discharge electrodes, wherein a
stability of an electrical resistance of the transparent conductive film
is lower at one end portion than at the other end portion of the tube; and
an ultraviolet decreasing film coated on the transparent conductive film,
said ultraviolet decreasing film having a higher ultraviolet decreasing
capability at one end portion than at the other end portion of the tube.
6. A low-pressure mercury vapor discharge lamp according to any one of
claims 1 to 5, wherein said transparent conductive film has a central
portion which has a thickness larger than a thickness at either end
portion thereof.
7. A low-pressure mercury vapor discharge lamp according to any one of
claims 1 to 5, wherein said transparent conductive film has a central
portion which has an electric resistance smaller than that at either end
portion thereof.
8. A low pressure mecury vapor discharge lamp according to any one of
claims 1 to 5, wherein said transparent conductive film has a maximum
thickness equal to or less than 100 nm.
9. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of a tin oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, said transparent conductive film
including an antimony a concentration of which is in the range of 0.8 to
2.0 mol % at both the end portions of the tube and the concentration of
which is in the range of 0.2 to 1.0 mol % at a central portion thereof,
and an electric resistance at both the end portions of the tube is made
higher than that at the central portion thereof.
10. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of a tin oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, said transparent conductive film
including an antimony a concentration of which is in the range of 0.8 to
2.0 mol % at both the end portions of the tube and the concentration of
which is in the range of 0.2 to 1.0 mol % at a central portion thereof,
and an electric resistance at both the end portion of the tube is made
higher than that at the central portion thereof; and
a phosphor film coated on in inside surface of the transparent conductive
film inside the tube.
11. A low-pressure mercury vapor discharge lamp according to claim 9 or 10,
wherein said transparent conductive film has a thickness at both the end
portions of the tube thinner than that at the central portion thereof.
12. A low-pressure mercury vapor discharge container according to claim 9
or 10, wherein the thickness of the transparent conductive film at each of
both the end portions of the tube is equal to or less than 25 nm.
13. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube; and
a transparent conductive film formed of metallic oxide mainly containing
tin oxide including antimony of 0.7 to 2.0 mol % and coated on an inner
surface of the tube between the electrodes, wherein said transparent
conductive film has a central portion having a thickness equal to or less
than 100 nm and both end portions each having a thickness equal to or less
than 25 nm and wherein the central portion of said transparent conductive
film has the thickness thicker than that of each of the end portions and
the transparent conductive film has a resistance of 2 k.OMEGA. to 50
k.OMEGA. per 10 cm of a longitudinal length of the tube at the central
portion thereof and a resistance of 20 k.OMEGA. to 1000 k.OMEGA. per 10 cm
of the longitudinal length of the tube at each of the end portions
thereof.
14. A low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube; and
a transparent conductive film formed of metallic oxide mainly containing
tin oxide including antimony of 0.7 to 2.0 mol % and coated on an inner
surface of the tube between the electrodes, wherein said transparent
conductive film has a central portion having a thickness equal to or less
than 100 nm and both end portions each having a thickness equal to or less
than 25 nm and wherein the central portion of said transparent conductive
film has the thickness larger than that of each of the end portions and
the transparent conductive film has a resistance of 2 k.OMEGA. to 50
k.OMEGA. per 10 cm of a longitudinal length of the tube at the central
portion thereof and a resistance of 20 k.OMEGA. to 1000 k.OMEGA. per 10 cm
of the longitudinal length of the tube at each of the end portions
thereof; and
a phosphor film formed on an inside surface of said transparent conductive
film.
15. A low-pressure mecury vapor type discharge lamp according to claim 14,
wherein the central portion of the transparent conductive film of the
container has a resistance higher than that of each of the end portions
thereof.
16. An illuminating apparatus according to any of claims 1-5, 9-10, or
13-14, comprising:
a main illuminating unit;
a low-pressure mercury vapor discharge lamp attached to the main
illuminating unit; and
a discharge lamp lighting device mounted on the main illuminating unit for
driving the low-pressure mercury vapor discharge lamp.
Description
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates to a discharge lamp particularly of
low-pressure mercury vapor typically represented by a fluorescent lamp
having transparent conductive film coated on the inner surface of the lamp
bulb and and also relates to an illuminating apparatus utilizing the same.
2. Description of The Related Arts
A low-pressure mercury vapor discharge lamp typically represented by a
fluorescent lamp, such as a rapid-start type fluorescent lamp, has a bulb
having an inner surface on which a transparent conductive film having tin
oxide is formed as a main component thereof.
The formation of the transparent conductive film of tin oxide is performed,
for example, by a spray method in which a tin chloride solution is sprayed
or by a so-called CVD method in which vapor of tin oxide is sprayed on the
inner surface of the bulb.
Since such a fluorescent lamp offers an excellent starting characteristic
and needs no starter lamp, it is widely used in offices, department stores
and the like. The rapid-start type fluorescent lamp, however, tends to
suffer from yellowish-brown band deposits (hereinafter referred to as
"yellowing") and blackening caused on the bulb inner surface in the
vicinity of electrodes, for example portions apart from the electrodes by
10 to 30 cm, when it is used for a long time such as about more than 1000
hours. Fluorescent lamps that have no transparent conductive film suffers
blackening as well. In this type fluorescent lamp, during the use thereof,
electrode materials are sputtered and stuck onto a phosphor film where
they react with mercury or phosphor, subsequently leading to blackening.
In the rapid-start type fluorescent lamps, however, the yellowing and
blackening in the vicinity of the electrodes are attributed to reasons
other than the sputtering of electrode materials.
Many papers or publications are known that have analyzed the cause for
yellowing and blackening typical of the rapid-start type fluorescent
lamps. According to them, why yellowing and blackening take place is
roughly summarized as follows. That is, a fluorescent lamp lights on AC
supply, microscopic discharges takes place between the transparent
conductive film, and electrodes at the moment the polarity is reversed.
The microscopic discharges cause the transparent conductive film to change
in quality. Mercury stuck onto the phosphor film coating near the
electrodes forms a discharge path. Thus, phosphor coating to which mercury
sticks is damaged by high energy of the discharge, the phosphor film
coating itself reacts with mercury, and furthermore, mercury reacts with
the transparent conductive film.
To restrict the generation of the yellowing and blackening phenomenon,
microscopic discharge likely to cause them must be controlled. A method
known to control the discharge is that the electrical resistance of the
transparent conductive film is set higher near the electrodes, as
disclosed, for example, in Japanese Patent Application Laid-open No.
56-84861.
More concretely, in the above prior art document of No. 56-84861, there is
disclosed a technique for changing a resistance distribution of a
transparent conductive film, in which a resistance at a bulb central
portion per unit length in the bulb axial direction is made low and a
resistance at bulb end portions near the electrodes is made high to obtain
substantially V-shaped resistance distribution of the conductive film
between the electrodes of the lamp to thereby suppress a minute discharge
near the electrodes. Such technique has been applied to commercially sold
rapid-start type fluorescent lamps, in which a resistance at the central
portion of the bulb is about 2 k.OMEGA. to 50 k.OMEGA. per 10 cm along the
axial length thereof and is about 20 k.OMEGA. to 500 k.OMEGA. per 10 cm
along the axial length thereof. In such fluorescent lamps, in order to
obtain the V-shaped resistance distribution, the film thickness of the
conductive film is changed on the inner surface of the bulb. In the
disclosed example, the conductive film is formed by introducing vapor of
tin compound and reacted therein so as to deposit the tin oxide on the
inner surface of the bulb. In this operation, since a reaction speed is
changed in an exponential function with respect to a bulb temperature, the
thickness of the conductive film is increased by making high the
temperature at the central portion of the bulb.
However, in the conventional technology, since the bulb temperature is made
high to supply the tin compound vapor by an amount more than required, the
reaction of the conductive film and the production speed thereof are made
faster, but an un-reacted tin compound remains, making coarse the film
condition. Such un-reacted tin compound is gradually reacted during the
lighting. It is also found that, due to the reaction after depositing of
the film, the film provides a large gap ratio and less elaboration in
density, and accordingly, the thickness of the film is made thick even in
the same deposited amount and the same resistance. Moreover, since the
undecomposed tin compound is reacted and decomposed during the lighting of
a fluorescent lamp, as a product, the resistance of the transparent
conductive film is gradually lowered during the use of the fluorescent
lamp and, hence, angle of the V-shaped resistance distribution is widened,
thus liably causing the blackening phenomenon to the lamp. Furthermore,
there causes a case where impure gas is produced through the decomposing
reaction of the tin compound, damaging the startability of the fluorescent
lamp.
In another method such as disclosed in Japanese Patent Application
Laid-open No. 57-32561, there is shown a technique for stabilizing the
resistance distribution of the transparent conductive film by adding an
additive such as antimony to the conductive film. In this technique,
however, it is intended to stabilize the resistance distribution only at
the production starting time, and accordingly, it is difficult to obtain a
proper resistance distribution of V-shape by adding the antimony.
A further method is that an electrically insulating film is coated on the
transparent conductive film, as disclosed, for example, in Japanese Patent
Application Laid-open No. 50-12885, Japanese Patent Application Laid-open
No. 52-49683, Japanese Patent Application Laid-open No. 52-93184, and
others.
The prior art quoted above are able to control the generation of the
yellowing and blackening to some degree. In the course of the study of
this problem, the inventors have found that, when the transparent
conductive film is thinned, some difference is caused in the degree of
yellowing and blackening generated even with apparently the same design
conditions. Specifically, in some lamps, the yellowing and blackening are
more noticeable on one side than on the other side of the lamp, while in
other lamps yellowing and blackening take place on both the left- and
right-hand sides in a balanced manner and are generally less noticeable.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or
drawbacks encountered in the prior art and to provide a low-pressure
mercury vapor discharge lump typically represented by a rapid-start type
fluorescent lamp capable of suppressing yellowing and blackening on its
left-hand and right-hand sides appearing in an unbalanced manner and also
provide an illuminating apparatus provided with such discharge lamp.
Another object of the present invention is to provide a low-pressure
mercury vapor discharge lamp typically represented by a rapid-start type
fluorescent lamp capable of providing a desired resistance distribution of
a transparent conductive film formed on an inner surface of a container
bulb of the lamp during the life time thereof and also capable of
maintaining a high starting capability with reduced yellowing and
blackening during the life time thereof and also provide an illuminating
apparatus provided with such discharge lamp.
In order to achieve the above objects, the inventors of this application
have conducted a variety of tests, for example, by taking into
consideration that the cause of left-right unbalanced yellowing and
blackening lies in the manner of forming of the transparent conductive
film and the phosphor film.
The test results have confirmed that the yellowing and blackening are
likely to happen (1) when the thickness of the transparent conductive film
differs greatly between near the left-hand-side electrode and near the
right-hand-side electrode, and thus, electrical resistance of the
transparent conductive film differs greatly between on the left-hand and
right-hand sides of the lamp, or (2) when the thickness of the phosphor
film differs greatly between both sides of the lamp.
In the analysis of properties of the transparent conductive film, its
resistance profile caught attention while its thickness profile was
largely ignored. This may be attributed to the fact that since the
thickness of the transparent conductive film is about 100 nm, accurate
gaging of the thickness has been difficult and therefore even gaging the
thickness has not been considered at all. Furthermore, the entire
transparent conductive film has been relatively thick, and thus, thickness
difference between both left- and right-hand sides has not been considered
to essentially affect the performance of the lamp.
In view of the above, the inventors measured the thickness of the
transparent conductive film using fluorescent X-ray technique.
Specifically, the relationship between thickness and the fluorescent X-ray
strength is determined using a material with its thickness known.
Fluorescent X-ray measurements were made to the transparent conductive
film, and then the results were referenced to the determined relationship
to calculate the thickness of the transparent conductive film.
As a result of the measurements, it was found that, when when thickness
criteria of the transparent conductive film in lamp manufacturing is set
to a thin gage, the lamp performance is subjected to substantial
variations and these performance variations lead to the generation of the
yellowing and blackening phenomenon, and the thicker the transparent
conductive film the more likely yellowing and blackening take place.
The inventors have continued their study to answer the question why the
thicker the transparent conductive film the more likely yellowing and
blackening take place. It has been thought that, when the transparent
conductive film is thick, a film forming material remains undecomposed
accordingly. While the lamp is in service, this undecomposed material is
gradually decomposed, causing electrical resistance of the transparent
conductive film to be decreased. As a result, the lamp tends to suffer
from microscopic discharge. It has been also thought that an energy source
consumed to decompose the undecomposed material is supplied by an
ultraviolet rays that transmits the phosphor film.
Based on the above thinking and in view of the fact that ultraviolet ray
absorption depends on the thickness of the phosphor film, the inventors
have invented the arrangement which prevents the ultraviolet rays from
reaching the transparent conductive film. The present invention is also
applied to a fluorescent lamp that contains discharge medium other than
mercury.
The aforementioned objects and other objects can be achieved in one aspect
of the present invention by providing a low-pressure mercury vapor
discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, the transparent conductive film having a
thickness on one end portion of the tube relatively thinner than a
thickness of the transparent conductive film on the other end portion of
the tube; and
a phosphor film coated inside of the transparent conductive film on an
inside surface of the tube, the phosphor film having a thickness on the
one end portion of the tube relatively thinner than a thickness of the
phosphor film on the other end portion of the tube.
The discharge medium is not limited to mercury-based one. It may be rare
gas, such as Xe, capable of emitting ultraviolet rays or Ne capable of
emitting a large quantity of visible light together with slight quantity
of ultraviolet rays.
The tubular light-transmitting tube may be constructed of soft glass, and,
depending on applications, of a silica glass as well. As a pair of
electrodes, either a hot cathode or a cold cathode will be utilized.
The metallic-oxide based, transparent conductive film, for example, may be
a film made of tin oxide that is rendered conductive by partially reducing
it or adding a tiny bit of antimony to it. Although metallic oxide is
inherently an insulator, the metallic-oxide based transparent conductive
film is obtained by adding additives to impart conductivity, by reducing
it. Also adding additives to enhance chemical stability or physical
strength is acceptable.
The inner surface means literally inner surface clear of any covering. The
phosphor film may be single-layered or multi-layered. The electrically
insulating film does not need to be capable of decreasing ultraviolet
rays.
The film thickness means averaged film thickness on an extended region on
each end of the lamp. Averaging is made to control variations involved in
thickness measurements. The extended region, for example, means the region
extended by 10 cm toward the direction of discharge from the electrode
that is most likely to suffer the yellowing and blackening phenomenon.
In another aspect of the present invention, there is provided a
low-pressure mercury vapor discharge lamp comprising;
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, the transparent conductive film having a
thickness on one end portion of the tube relatively thinner than a
thickness of the transparent conductive film on the other end portion of
the tube;
an ultraviolet decreasing film coated on an inside surface of the
transparent conductive film inside the tube; and
a phosphor film coated inside of the ultraviolet decreasing film, wherein a
combined thickness of the ultraviolet decreasing film and the phosphor
film on the one end portion of the tube is relatively thinner than a
combined thickness of the ultraviolet decreasing film and the phosphor
film on the other end portion of the tube.
The ultraviolet decreasing film is the film which decreases ultraviolet
rays from transmitting by absorption or reflection, and is typically a
laminate or continuous film of metallic oxide powder of ZnO, TiO.sub.2,
CsO, .alpha.-crystalline A1203.
In a further aspect of the present invention, there is provided a
low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof with a small quantity of an additive and coated on an inner
surface of the light-transmitting tube between the discharge electrodes,
wherein a content of the additive in the transparent conductive film on
one end portion of the tube is relatively greater than a content of the
additive in the transparent conductive film on the other end portion of
the tube; and
a phosphor film coated inside of the transparent conductive film on an
inside surface of the tube, the phosphor film having a thickness on the
one end portion of the tube relatively thinner than a thickness of the
phosphor film on the other end portion of the tube.
When the transparent conductive film is made of tin oxide which is
partially reduced to impart conductivity, antimony may be added to
stabilize conductivity. In this case, antimony added is an additive. A
variety of additives are acceptable as long as transparency and
conductivity are maintained.
In a still further aspect, there is provided a low-pressure mercury vapor
discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on the inner surface of the light-transmitting tube
between the discharging electrodes, wherein the transparent conductive
film has a thickness on one end portion of the tube relatively thinner
than a thickness of the transparent conductive film on the other end
portion of the tube and has a thickness on a middle portion of the tube
thicker than the thickness of the transparent conductive film on both end
portions of the tube; and
a phosphor film coated inside of the transparent conductive film on an
inside surface of the tube, wherein the phosphor film has a thickness on
the one end portion of the tube relatively thinner than a thickness on the
other end portion of the container and has a thickness substantially
gradually increasing from the one end portion to said other end portion of
the tube.
It is important that the thickness of the phosphor film generally gradually
increases from one end portion to the other end portion of the tube, and
"substantially gradually increases" means that a partial decrease in
thickness somewhere along the tube is acceptable.
In a still further aspect, there is provided a low-pressure mercury vapor
discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film coated on an inner surface of the
light-transmitting tube between the discharge electrodes with a stability
in electrical resistance of the transparent conductive film being lower on
one end portion than on the other end portion of the container; and
an ultraviolet decreasing film coated on an inside surface of the
transparent conductive film inside the container, the ultraviolet
decreasing film having higher ultraviolet decreasing capability on one end
portion than on the other end portion of the tube.
The stability of electrical resistance of the transparent conductive film
refers to the one against ultraviolet rays. For example, a decreased
stability of electrical resistance is noticed on the thicker portion of
conductive film where a decomposed material is contained more in amount
while an increased stability results on the thinner portion of conductive
film. In the tin-oxide based conductive film, the higher the concentration
of antimony as an additive, the higher electrical resistance of the film.
The ultraviolet decreasing film comprises phosphor film. The ultraviolet
decreasing film may be a laminate made of a single phosphor film and an
ultraviolet ray absorbing film.
In the above respective aspects, the transparent conductive film has a
central portion partially having a thickness thicker than a thickness of
each of both the end portions. The transparent conductive film has a
central portion partially having an electric resistance smaller than that
of each of both the end portions thereof. The transparent conductive film
has a maximum thickness equal to or less than 100 nm.
The ultraviolet decreasing film comprises phosphor film. The ultraviolet
decreasing film may be a laminate made of a single phosphor film and an
ultraviolet ray absorbing film.
When the middle portion is more thickly structured as stated above, the
middle portion does not necessarily mean the exact center of the tube
between both ends. Slight deviation of the middle portion toward either
end is acceptable.
The discharge lamp lighting device is a rapid-start type discharge starter.
According to the characteristics of the embodiments described above of the
present invention, the quantity of ultraviolet rays that reaches the
transparent conductive film through the thick portion of the phosphor film
is reduced. The transparent conductive film corresponding to the thick
portion of the phosphor film is also thick and contains more undecomposed
material. However, the reduced quantity of ultraviolet rays slows the
decomposition process of the undecomposed material and thus controls the
change in electrical resistance there. On the other hand, the quantity of
ultraviolet rays that reaches the transparent film through the thin
portion of the phosphor film is relatively large. However, the transparent
conductive film there is also thin, with a small amount of undecomposed
material contained, and thus, the change in electrical resistance remains
small. As a result, the change in electric resistance in the transparent
conductive film is balanced on both end portions of the container, and the
lamp is free from substantial yellowing and blackening phenomenon on one
particular end arising from a resistance change on that end.
In another aspect of the present invention, the transparent conductive film
is subjected to more change in electrical resistance on its thick portion
and less change on its thin portion. Both the ultraviolet decreasing film
and the phosphor film restrict ultraviolet rays transmission therethrough
that causes resistance change, and the thicker the overall thickness of
both films the more ultraviolet rays is restricted. The thick portion of
the transparent conductive film that is subjected to more resistance
change is coated with the thick portions of the ultraviolet decreasing
film and the phosphor film combined, which provide high ultraviolet
decreasing capability. The thin portion of the transparent conductive film
that is subjected to less resistance change is coated with the thin
portions of the ultraviolet decreasing film and the phosphor film
combined, which provide low ultraviolet decreasing capability. The change
in electrical resistance of the transparent conductive film is balanced on
both end portions of the container. The lamp is free from substantial
yellowing and blackening on one particular end arising from a resistance
change on that end.
In a further aspect of the present invention, the electric resistance in
the transparent conductive film is more stable where more additive is
contained therein. The thick portion of phosphor film is formed so that
the portion with less additive, thus provided with less stability in
electrical resistance, is exposed to less ultraviolet rays. The change in
electrical resistance in the transparent conductive film is balanced on
both end portions of the tube. The lamp is free from substantial yellowing
and blackening on one particular end arising from a resistance change on
that end.
In a still further aspect of the present invention, the quantity of
ultraviolet rays that reaches the transparent conductive film through the
thick portion of the phosphor film is reduced in the same manner described
above. The transparent conductive film corresponding to the thick portion
of the phosphor film is also thick, and contains more undecomposed
material. However, the reduced quantity of ultraviolet rays reached slows
the decomposition process of the undecomposed material and thus controls
the change in electrical resistance there. On the other hand, the quantity
of ultraviolet rays that reaches the transparent film through the thin
portion of the phosphor film is relatively large. However, the transparent
conductive film there is also thin, with a small amount of undecomposed
material contained, and thus, the change in electrical resistance remains
small. As a result, the change of electrical resistance in the transparent
conductive film is balanced on both end portions of the tube, and the lamp
is free from substantial yellowing and blackening on one particular end
arising from a resistance change on that end.
The phosphor film is typically formed by allowing phosphor suspension to
run in straight glass tube with the straight glass tube secured in an
upright position. Thus, the glass tube has phosphor film thinnest on its
top side (inside) and gradually thick as it runs downward. In view of
this, a high resistance side, that is, a thin end portion of the
transparent conductive film is formed corresponding to the thin portion of
the phosphor film on the top side of the tube, and a low resistance side,
that is, a thick end portion of the transparent conductive film is formed
corresponding to the thick portion of the phosphor film on the bottom side
of the tube. The change in electrical resistance in the transparent
conductive film is balanced on both end portions of the tube, and the lamp
is free from substantial yellowing and blackening on one particular end
arising from a resistance change on that end.
In a still further aspect of the present invention, the ultraviolet
decreasing film is arranged so that its higher ultraviolet decreasing
capability portion is formed on less resistance stabilized portion of the
transparent conductive film. The change in electrical resistance in the
transparent conductive film is balanced on both end portions of the tube,
and the lamp is free from substantial yellowing and blackening on one
particular end arising from a resistance change on that end.
The both end portions of the transparent decreasing film is relatively
thin, thus of a high resistance, and with less quantity of undecomposed
material that is the cause for resistance change in the life of the lamp.
The change in electrical resistance is restricted, and the yellowing and
blackening generations are thus effectively controlled.
The electrical resistance on both end portions of the transparent
conductive film is relatively large, and microscopic discharge is
restricted, effectively controlling the generation of the yellowing and
blackening.
The thickness of the transparent conductive film is entirely thin, and
balanced change of electrical resistance on both end portions is achieved,
effectively controlling the generation of the yellowing and blackening.
In a still further aspect of the present invention, there is provided a
low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, the transparent conductive film
including an additive wherein a containing ratio of the additive at both
the end portions of the tube is made higher than that at a central portion
thereof and an electric resistance at both the end portions of the tube is
made higher than that at the central portion thereof.
In this aspect, the light-transmitting tube is usually a glass bulb. The
transparent conductive film contains mainly a metallic oxide but includes
an additive, undecomposed compound, partially reduced metal or impurity,
and a mixture may be used as a metallic oxide. The amount of the additive
to be included is a small amount capable of applying electric conductivity
and utilizing for adjusting a resistance. Both the end portions of the
tube means portions in the vicinity of the electrodes apart from about 20
cm towards inside the tube and the central portion thereof means a portion
near the central portion of the discharge lamp. The amount of the additive
near the central portion may includes approximately zero.
In a still further aspect, there is provided a low-pressure mercury vapor
discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube;
a transparent conductive film formed of metallic oxide as a main component
thereof and coated on an inner surface of the light-transmitting tube
between the discharge electrodes, the transparent conductive film
including an additive wherein a containing ratio of the additive at both
the end portions of the tube is made higher than that at a central portion
thereof and an electric resistance at both the end portions of the tube is
made higher than that at the central portion thereof; and
a phosphor film coated inside of the transparent conductive film on an
inside surface of the tube.
In these aspect, the metallic oxide is a tin oxide and the additive is an
antimony, and the antimony containing ratio at both the end portions of
the tube is within 0.8 to 2.0 mol % and the antimony containing ratio at
the central portion of the container is within 0.2 to 1.0 mol %. In these
aspect, the transparent conductive film has a thickness at both the end
portions of the tube thinner than that at the central portion thereof. The
thickness of the transparent conductive film at each of both the end
portions of the tube is equal to or less than 25 nm.
According to the embodiments of these aspects, the concentration of the
additive in the transparent conductive film is made low at the central
portion thereof and made high at both the end portions thereof. Although
the metallic oxide essentially has an electrically insulative property,
the conductivity is created by partially reducing the metallic oxide or
adding the additive, and in the case of adding the additive, the
conductivity, i.e. resistance, less varies and stabilizes. Thus, the
resistance at the end portions at which the concentration of the additive
is stabilized, and the resistance at the central portion is not stabilized
because of low additive concentration and gradually lowers. That is, the
resistance at the central portion of the conductive film is positively
controlled so as not to be stabilized and the concentration of the
additive is made lower. Accordingly, the oxygen is released in the
light-transmitting tube to thereby lower the resistance of the transparent
conductive film, thus the resistance distribution approaching an ideal
V-shape.
Furthermore, according to these aspects of the present invention, tin oxide
as the main component of the transparent conductive film and antimony as
the additive are combined and such combination is widely utilized, thus
being reliable. In such combined use, a desired resistance distribution is
easily obtained with the antimony content of 0.8 to 2.0 mol % at the end
portions of the light-transmitting tube and of 0.2 to 1.0 mol % at the
central portion thereof. In the case of less than 0.8 mol % of the
antimony concentration, at the end portions of the tube, the resistance is
less stabilized, and on the contrary, in the case of more than 2.0 mol %,
the transmittance of the transparent conductive film is likely lowered
because of the increasing of the impurity. In the case of less then 0.2
mol % of the antimony concentration at the central portion of the tube,
the stabilizing degree of the resistance of the conductive film is
excessively lowered, whereby the resistance is hence liably lowered and a
small discharge is caused at the central portion of the tube, resulting in
the generation of the blackening phenomenon at this portion. In the case
of more than 1.0 mol % at the central portion, the resistance is
remarkably stabilized and it becomes difficult to obtain an ideal V-shaped
resistance distribution.
Furthermore, according to the aspect in which the film thickness at the end
portion of the tube is thinner than that at the central portion of the
tube, the film thickness is in reverse proportion to the resistance, so
that the ideal V-shaped resistance distribution can be obtained by
controlling the film thickness, and more ideal V-shaped resistance
distribution will be obtained by promoting the lowering of the resistance
at the central portion of the tube due to the concentration control of the
additive.
The film thickness of the transparent conductive film is made to less than
25 nm at the end portions of the tube, which is thinner than a film
thickness of a conventional conductive film of40 to 60 nm, so that an
undecomposed compound less remains and the resistance change during the
using of the lamp is hence made small. It is not necessary to make limit
the lower limit of the film thickness, but, in the case of less than 10
nm, a desired conductivity will be hardly achieved.
In a still further aspect of the present invention, there is provided a
low-pressure mercury vapor discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube; and
a transparent conductive film formed of metallic oxide mainly containing
tin oxide including antimony of 0.7 to 2.0 mol % and coated on an inner
surface of the container between the electrodes, wherein the transparent
conductive film has a central portion having a thickness equal to or less
than 100 nm and both end portions each having a thickness equal to or less
than 25 nm and wherein the central portion of the transparent conductive
film has the thickness larger than that of each of the end portions and
the transparent conductive film has a resistance of 2 k.OMEGA. to 50
k.OMEGA. per 10 cm of a longitudinal length of the tube at the central
portion thereof and a resistance of 20 k.OMEGA. to 1000 k.OMEGA. per 10 cm
of the longitudinal length of the tube at each of the end portions
thereof.
In this aspect, the light-transmitting tube is usually a glass bulb. The
transparent conductive film contains mainly a metallic oxide but includes
an additive, undecomposed compound, partially reduced metal or impurity,
and a mixture with another metallic compound including a relatively much
tin oxide may be used. The amount of the additive to be included is a
small amount capable of applying electric conductivity and utilizing for
adjusting a resistance. Both the end portions of the tube means portions
in the vicinity of the electrodes apart from about 20 cm towards inside
the tube, and the central portion thereof means a portion except the end
portions. The amount of the additive means a mean value at the respective
portions.
In a still further aspect, there is provided a low-pressure mercury vapor
discharge lamp comprising:
a light-transmitting tube containing discharge medium and having
longitudinal end portions;
a pair of discharge electrodes each mounted in a vicinity of the respective
end portions of the tube; and
a transparent conductive film formed of metallic oxide mainly containing
tin oxide including antimony of 0.7 to 2.0 mol % and coated on an inner
surface of the tube between the electrodes, wherein the transparent
conductive film has a central portion having a thickness equal to or less
than 100 nm and both end portions each having a thickness equal to or less
than 25 nm and wherein the central portion of the transparent conductive
film has the thickness larger than that of each of the end portions and
the transparent conductive film has a resistance of 2 k.OMEGA. to 50
k.OMEGA. per 10 cm of a longitudinal length of the tube at the central
portion thereof and a resistance of 20 k.OMEGA. to 1000 k.OMEGA. per 10 cm
of the longitudinal length of the tube at each of the end portions
thereof; and
a phosphor film formed on an inside surface of the transparent conductive
film.
In these aspects, the central portion of the transparent conductive film of
the container has a resistance higher than that of each of the end
portions thereof.
According to these aspects of the present invention, the transparent
conductive film has the central portion having a thickness thinner than
that of the end portions thereof and the central portion has a resistance
in a predetermined range, so that a fine V-shaped resistance distribution
with less blackening can be obtained. Furthermore, since the antimony
concentration is within 0.7 to 2.0 mol %, the resistance change of the
transparent conductive film during the use of the lamp is made small in
comparison with the case of less than 0.7 mol % of the antimony
concentration. Further, the lowering of the light transmittance due to the
addition of the antimony can be effectively suppressed because the
antimony concentration does not exceed 2.0 mol %. In this range of the
antimony concentration, the resistance of the transparent conductive film
approaches substantially minimum value or near, thus being capable of
forming the transparent conductive film with thin thickness.
Still furthermore, the transparent conductive film of these embodiments is
formed thinner than a conventional transparent conductive film. That is,
the end portion thereof has a thickness of less than 25 nm, which is
thinner than that of the conventional one of40 to 60 nm. Concerning the
central portion of the transparent conductive film, it has a thickness of
less than 100 nm in comparison with a conventional one having a thickness
of more than 100 nm at the central portion. Since the transparent
conductive film of the present embodiment has uniform resistance and
thickness, it has small gap ratio and fine structure, so that the
undecomposed compound less remains in the film, thus effectively
suppressing the resistance change during the use of the lamp. Such
advantageous effect is not expected by the conventional formation of the
transparent conductive film having a large gap ratio. Furthermore, the
transparent conductive film of the present embodiment is less reacted and
decomposed after the completion of the product lamp, so that the
generation of impurity due to the decomposing reaction can be suppressed
in minimum, thus obtaining a good startability of the lamp.
In a still further aspect of the present invention, there is provided an
illuminating apparatus comprising:
a main illuminating unit;
a low-pressure mercury vapor discharge lamp, of the characters described
above in the respective aspects, attached to the main illuminating unit;
and
a discharge lamp lighting device mounted on the main illuminating unit for
driving the low-pressure mercury vapor type discharge lamp.
The discharge lamp lighting device is a rapid-start type discharge starter.
The illuminating apparatus provided with the low-pressure mercury vapor
discharge lamp having characteristic features described above can attain
substantially the same effects and advantages as those described
hereinabove.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1A is a front view showing an embodiment of a low-pressure mercury
vapor discharge lamp according to the present invention;
FIG. 1B is an partially enlarged view of the lamp, encircled by 1B, of FIG.
1A;
FIG. 2 is an illustrated view showing a manufacturing process of a
transparent conductive film of the discharge lamp of FIG. 1;
FIG. 3 is a front view showing an illuminating apparatus provided with the
discharge lamp of FIG. 1;
FIG. 4 is a cross-sectional view showing the discharge lamp of FIG. 1;
FIG. 5A is a graph showing a relationship between a thickness and an
electrical resistance of the transparent conductive film of the discharge
lamp of the embodiment;
FIG. 5B is a graph showing the thickness profile of a phosphor film of the
embodied discharge lamp;
FIG. 5C is a graph showing the thickness profile of an insulator film
(protection film) of the embodied discharge lamp;
FIG. 5D is a graph showing the distribution of an additive content in the
transparent conductive film of the embodied discharge lamp;
FIG. 5E is an illustration of the discharge lamp of this embodiment having
the longitudinal length corresponding to the axes of abscissa of FIGS. 5A
to 5D;
FIG. 6 is a graph showing a relationship between a resistance distribution
of a transparent conductive film of a low-pressure mercury vapor discharge
lamp of another embodiment of the present invention and a position of the
transparent conductive film in its longitudinal direction;
FIGS. 7A and 7B are illustrated views showing another manufacturing process
of a transparent conductive film of the discharge lamp of FIG. 1 according
to another embodiment of the present invention;
FIG. 8 is a graph showing a relationship between antimony concentration and
relative resistance of a transparent conductive film of a low-pressure
mercury vapor discharge lamp of further embodiment of the present
invention;
FIG. 9 is a graph showing a relationship between antimony concentration and
relative resistance change of a transparent conductive film of a
low-pressure mercury vapor discharge lamp of further embodiment of the
present invention;
FIG. 10 is a graph showing a relationship between antimony concentration
and full-light transmittance of a transparent conductive film of a
low-pressure mercury vapor discharge lamp of the further embodiment of the
present invention;
FIG. 11 is a graph showing a relationship between a film thickness of a
transparent conductive film of a low-pressure mercury vapor discharge lamp
of the further embodiment of the present invention and a generation of the
blackening to the bulb of the discharge lamp after the lighting time of
5000 hour at various portions from electrodes; and
FIG. 12 is a graph showing a relationship between an average film
thickness, at a portion near the electrode, of a transparent conductive
film of a low-pressure mercury vapor discharge lamp of the further
embodiment of the present invention and a generation of the blackening to
the bulb of the discharge lamp after the lighting time of 5000 hour at
various portions from electrodes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, preferred embodiments of the present invention
are discussed, in which FIGS. 1 to 3 are commonly utilized for the
respective embodiments.
FIG. 1 is a front view showing a first embodiment of the fluorescent lamp
as one typical example of a low-pressure mercury vapor discharge lamp of
the present invention, and FIG. 1B is a cross-sectional view showing an
enlarged view of the portion 1B in FIG. 1A. The basic construction in FIG.
1A meets with with FLR40S.W/M specified in Japanese Industrial Standards
(JIS). The fluorescent lamp has a pair of discharging electrodes 2
including filaments, sealed in a tubular light-transmitting sealed
container, that is, a glass bulb or tube 1 with each electrode supported
on a longitudinal end of the bulb 1. Support leads which support filaments
pass through the glass bulb 1 in an air-tight manner and are connected to
lamp pins 3a which are projected out of caps 3 at both end of the glass
bulb 1. Contained inside the glass bulb 1 are a small quantity of mercury
and argon of 266 to 400 Pa (2 to 3 Torr).
The inner surface of the glass bulb is coated with a transparent conductive
film 4. The transparent conductive film 4 contains tin oxide as its main
component and a part of tin oxide is reduced to impart conductivity to the
transparent conductive film. The transparent conductive film also contains
a tiny bit of antimony to stabilize the conductivity. Antimony having a
valence of 3 that is replaced with tin having a valence of 4 in the
transparent conductive film 4 imparts conductivity as reduced tin oxide
does.
The antimony content in the transparent conductive film 4 is 1.5 mol % on
both end portions and 0.7 mol % on its middle portion.
The transparent conductive film 4 is 10 nm thick on the right-hand end
portion R and left-hand end portion L, and 60 nm thick on its middle
portion. Preferably, thickness on both end portions is 25 nm or less, and
that on the middle portion is 100 nm or less. Thickness is determined on
the calibration curve of Sn strength of fluorescent X-ray as already
mentioned. An electrical resistance of the transparent conductive film 4
per unit length (10 cm) along the direction of length is 200 .OMEGA. on
the right-hand end portion R, 300 .OMEGA. on the left-hand end portion L,
and 1 K.OMEGA.on the middle portion.
Coated on top (inside surface) of the transparent conductive film 4 is an
electrically insulating film 5 which is a laminate made of aluminum oxide
powder. The insulator film 5 has no ultraviolet absorbing capability. The
diameter of aluminum oxide powder particles ranges from 0.05 to 0.1 .mu.m.
The average thickness of the insulator film 5 on both end portions is 1 to
3 .mu.m, while the thickness on the right-hand end portion R is relatively
thicker than that on the left-hand end portion L. The insulator film 5
keeps mercury out of contact with the transparent conductive film 4 so
that mercury may not react with tin or antimony in the transparent
conductive film 4. The insulator film 5 thus prevents the transparent
conductive film 4 from changing in quality. The insulator film 5 performs
a function of restricting microscopic discharge because of its
electrically insulating nature.
Coated on top (inner surface) of the insulator film 5 is a phosphor film 6
that faces a discharge path. The phosphor film 6 contains antimony,
manganese, and keep-alive halo-calcium phosphor as its main components.
The phosphor film 6 is about 35.mu.m thick on the right-hand side portion
R, and about 25 .mu.m on the left-hand side portion L. Rare earth
phosphors used in the recently widely used three band fluorescent lamp
specified in Japanese Industrial Standards (JIS) are also acceptable as
phosphor film material. Thicknesses of the insulator film 5 and the
phosphor film 6 are determined by using a known fluorescent X-ray method.
The transparent conductive film 4 is manufactured in the following
procedure. FIG. 2 is a diagram showing the manufacturing process of the
transparent conductive film. A tubular glass bulb 1 opened at both ends is
prepared. The glass bulb 1 held at its horizontal position is put into a
heating oven, and then heated. The glass bulb is heated on its middle
portion at about 560.degree. C., and on its end portions at about
500.degree. C. In this state, mixed vapors of tin tetrachloride and
antimony trichloride are introduced into the glass bulb 1 through one
opening, and then pushed out of the glass bulb 1 through the other
opening. This process allows dimethyltin dichloride and antimony
trichloride to be put into contact with heated glass bulb 1, and then
decomposed, oxidized, and then deposited in the form of tin oxide and
antimony oxide onto the inner surface of the glass bulb 1. The molar ratio
of dimethyltin chloride to antimony trichloride is approximately 99.3:0.7.
This ratio determines the antimony content in the transparent conductive
film 4 on the middle portion of the glass bulb 1 in its finished state.
On both end portions of the glass bulb 1, heating temperature is relatively
low enough to slow the rate of reaction, and thus part of the supplied
vapors allowed to pass without reacting, out of the other opening of the
bulb 1. Since a high pressure vapor is easily pushed out compared with a
low pressure vapor, the low pressure vapor material reacts and deposits
more on the low heating temperature portions. The vapor pressure of
dimethyltin chloride (the vapor pressure of tin chloride immediately
before decomposition and deposit) is higher than that of antimony
trichloride, and thus, the antimony content of the deposit on both ends is
higher than the antimony content of the mixed vapor. In contrast, on the
middle portion of the bulb 1, the supplied vapors react and deposit as it
is, and the antimony content of the deposit there is equal to the antimony
content in the supplied vapor. As a result, the antimony content on the
middle portion of the bulb 1 is thus lower than that on both end portions
of the bulb 1. The difference in heating temperature cause not only the
difference in the antimony content but also a thickness difference, and
thus, a thick portion on the middle of the bulb 1 and a thin portion on
both ends because of the difference of resulting quantity of deposit. The
thickness profile is formed so that electrical resistance on the middle
portion is low.
Even if the supply side of the bulb for the vapor (on the right-hand side
R) and the discharge side of the bulb (on the left-hand side L) are heated
for reaction under the same temperature, both sides are different in the
quantity of deposit with a thick deposit formed on the supply side and a
thin deposit on the discharge side. This is because the discharge side is
naturally short of materials for deposits.
If no difference is desired in the antimony content from location to
location, the vapor of dimethyl dichloride and antimony trichloride is
allowed into the bulb 1 to undergo decomposition process for film forming
while the middle portion and both end portions of the bulb 1 are heated at
a temperature of 500.degree. C. for a predetermined time. After that, the
middle portion of the bulb 1 is heated at a temperature of 500.degree. C.
to complete the transparent conductive film 4.
When it is required to provide a difference in the antimony content between
on the left-hand end portion L and on the right-hand end portion,
different heating temperatures will be applied to both end portions. In
this case, however, the antimony content on the left-hand end portion
where the thin portion of the phosphor film 6 is applied is preferably set
higher than that on the right-hand end portion. This helps to stabilize
electrical resistance on the left-hand end portion L which is exposed more
to ultraviolet rays which causes resistance change in the transparent
conductive film 4.
Different types of compounds containing tin and antimony result in
different vapor pressures within heating temperature range, and thus, the
antimony content on both end portions is set lower than that on the middle
portion in the transparent conductive film 4.
The insulator film 5 is coated on top of the transparent conductive film 4
by coating, on the transparent conductive film 4 inside the bulb 1, a
coating solution containing aluminum oxide power and then by drying the
same. Next, the bulb 1 is coated with the phosphor coating solution. After
allowing the phosphor coating to dry, it is then sintered. The discharging
electrodes 2 are mounted on both ends of the glass bulb 1. The glass bulb
1 is then evacuated through an exhaust pipe while the interior of the bulb
1 is heated. A small quantity of mercury and argon are introduced into the
bulb 1 and the bulb 1 is then completely sealed. The caps 3 are mounted on
both ends of the bulb 1. Lead wires are connected to pins 3a. This
concludes the manufacturing process of the fluorescent lamp.
Each of the phosphor coating solution and the aluminum-oxide powder
containing solution is applied by running from top down inside the bulb 1
that has already the transparent conductive film 4 coated. In this
operation, the bulb 1 is held in an upright position wherein positioned on
top is the left-hand end portion L which has the thin portion of the
transparent conductive film 4 compared to the right-hand end portion.
Then, each coating is allowed to dry. When each of the coating solutions
is run from top down inside the bulb 1 in its upright position, the top
side of the bulb 1, namely, the left-hand end portion L is thinly formed
compared to the right-hand end portion R.
The fluorescent lamp thus processed is mounted on an illuminating apparatus
main unit 20 which is equipped with circuit components 22 such as ballast
for starter circuit of the rapid-start fluorescent lamp. The illuminating
apparatus main unit 20 is also provided with sockets 21 that mechanically
hold and electrically connects the fluorescent lamp.
FIG. 5 shows diagrammatically thickness profiles of the transparent
conductive film 4, the insulator film 5, and the phosphor film 6, and the
content profile of an additive such as antimony. As seen from FIG. 5A, the
electrical resistance of the transparent conductive film 4 is inversely
proportional to the thickness of the transparent conductive film 4.
When the fluorescent lamp thus processed is driven by an ordinary starter
device, thermoelectrons emitted by a discharging electrode filament
functioning as a cathode travel via the transparent conductive film 4 and
reach another discharging electrode filament functioning as an anode, thus
forming a discharge path. The lamp immediately lights, and a light in a
given band is emitted through the phosphor film 6.
While the lamp lights, microscopic discharges take place between mercury
particles in the bulb 1 and the transparent conductive film 4. This causes
the phosphor film 6 between the transparent conductive film 4 and a plasma
discharge path to break down and the tin oxide to react with mercury,
leading to yellowing and blackening near discharge electrode filaments.
According to the present invention, however, the generations of the
yellowing and blackening are balanced between on the left-hand end portion
and on the right-hand end portion, and become substantially less visible
compared with conventional fluorescent lamps. Furthermore, the fluorescent
lamp offers a slowed reduction in light flux within service life.
The mechanism for preventing the yellowing and blackening is thus
summarized as follows. Since the thick portion of the phosphor film 6 is
coated on the inside surface of the transparent conductive film 4 on the
right-hand end portion R where more undecomposed material remains after
the film forming, the thick portion of the phosphor film 6 absorbs
relatively more ultraviolet rays, thus transmitting less ultraviolet rays,
compared with the opposite situation (where the thin portion of the
phosphor film is coated on the inside surface of the thick portion of the
transparent conductive film) while the lamp is operated. This arrangement
restricts the reaction of the ultraviolet rays with undecomposed material
that is more on the right-hand end portion of the transparent conductive
film 4. The thick portion also makes the yellowing and blackening less
visible.
In the thin portions of the transparent conductive film 4 and the phosphor
film 5, the rate of reaction during use is small because there is less
undecomposed material in the transparent conductive film 4 even if the
thin portion of the phosphor film 6 allows more ultraviolet light to
transmit therethrough. This arrangement keeps the change in electrical
resistance to a minimum value, and even if the yellowing and blackening
are as marginal as those on the other side and substantially less visible
as a whole. In the above embodied fluorescent lamp according to the
present invention, the inner surface of the bulb 1 is coated with the
transparent conductive film 4, the electrically insulating film 5, and the
phosphor film 6. Alternatively, the insulator film 5 is dispensed with.
The fluorescent lamp without the insulator film 5 has performed equally as
good as the fluorescent lamp with the insulator film 5.
The inventors have produced and tested a variety of lamps with films
according to the present invention and other types of films in order to
study further lamp characteristics in terms of the yellowing and
blackening and the rate of reduction in light flux.
A first test lamp is an FLR40W lamp having an inner surface coated with the
transparent conductive film 4, aluminum oxide powder containing film as
the insulator film 5, and halo-calcium phosphate phosphor as the phosphor
film 6 in that order. A second test lamp is identical to the first test
lamp except that a three-band phosphor replaces halo-calcium phosphate
phosphor as the phosphor film 6. A third test lamp is also identical to
the first lamp except that the insulator film 5 is dispensed with. A
fourth test lamp is identical the second test lamp except that the
insulator film 5 is dispensed with. The second through fourth test lamps
are all identical to the first test lamp otherwise noted above.
A first comparative lamp through a fourth comparative lamp are identical to
the first through fourth test lamps, respectively, except that in all
comparative lamps the thick portion of the transparent conductive film 4
is reversed. In the comparative lamps, the thick portion and the thin
portion of the phosphor film 6 correspond to the thin portion and the
thick portion of the transparent conductive film 4, respectively.
These lamps were subjected to the continuous running test in which the
specimens were checked for the yellowing and blackening, and the reduction
in light flux have been checked at the moment of 3000-hour and 5000-hour
points. The reduction rate in light flux is referenced to 0-hour starting
point. The following Table shows the test results. In the table,
.largecircle. denotes excellent, .DELTA. denotes acceptable and X denotes
poor.
TABLE
______________________________________
Test Yellow- Black- Light flux rate
lamp Film structure
ing ening 3000 H
5000 H
______________________________________
1st lamp
Trans. cond. .smallcircle.
.smallcircle.
95% 93%
film: Alumina
Insul. film:
1st com.
Halo-phosphate
x .DELTA.
92% 91%
lamp Phosphor film
2nd lamp
Trans. cond. .smallcircle.
.smallcircle.
95% 94%
film: Alumina
Insul. film:
2nd com.
3 band phosphor
x .DELTA.
92% 91%
lamp Phosphor film
3rd lamp
Trans. cond. .smallcircle.
.smallcircle.
94% 92%
film: Alumina
3rd com.
Halo-phosphate
x x 90% 89%
lamp Phosphor film
4th lamp
Trans. cond. .smallcircle.
.smallcircle.
93% 92%
film: Alumina
4th com.
3 band phosphor
x .DELTA.
91% 90%
lamp Phosphor film
______________________________________
As seen from Table, the lamps (test lamps) according to present invention
suffer less yellowing and blackening and give satisfactory reduction rate
of light flux.
The present invention is not limited to the above embodiment. For example,
the insulator film 5 may be of a type that has an ultraviolet decreasing
capability such as those constructed of ZnO, TiO.sup.2, CsO. The
ultraviolet decreasing insulator 5 screens more effectively the
ultraviolet rays that would change the electrical resistance, thus
stabilizing electrical resistance of the transparent conductive film 4. In
this case, the thickness profile of the insulator 5 is designed to agree
with those of the phosphor film 6 and the transparent conductive film 5.
It is contemplated that the thickness profile of the insulator 5 having the
ultraviolet decreasing capability is designed opposite to that of the
phosphor film 6. In this case, both the insulator film 5 and the phosphor
film 6 are considered as a combined film, and then either end portion that
has a higher ultraviolet decreasing capability (namely, the larger
combined thickness side) is coated on the thick portion of the transparent
conductive film 4. Then, equally effective results may be obtained.
Furthermore, alternatively, xenon (Xe) may substitute for mercury as a
discharge gas. Xenon emits a high level of ultraviolet rays which varies
greatly the electrical resistance of the transparent conductive film 4.
This leads to microscopic discharges in the vicinity of discharge
electrodes, a diversity of reactions with phosphor and glass would be
triggered By microscopic discharges, though no reaction with mercury takes
place. Deterioration in appearance and light flux would take place. The
use of the present invention, however, controls the above problems.
Spray method may be used to form a transparent conductive film. To take
advantage of the present invention, the resistance profile of the
transparent conductive film 4 is not limited to a V-shaped curve.
Furthermore, concerning the low pressure mercury vapor type discharge lamp,
i.e. fluorescent lamp, of another embodiment, in which FIGS. 1 to 3 are
commonly applied, the resistance distribution of the transparent
conductive film 4 of the fluorescent lamp was measured at times of (a)
just after the formation of the conductive film 4, (b) just after the
completion of a fluorescent lamp as a product, and (c) after the 1000 hour
lighting time, and the resistance distribution of a transparent conductive
film of a conventional fluorescent lamp was also measured at times of (e)
just after the formation of the conductive film 4, (f) just after the
completion of a fluorescent lamp as a product, and (g) after the 1000 hour
lighting time. Antimony was not added to the transparent conductive film
4, which has a film thickness of about 50 nm at its ends and of about 100
nm at its central portion of the bulb. The measured results are shown in
FIG. 6, in which the abscissa axis represents a position in a fluorescent
lamp and the ordinate axis represents a resistance per unit length, i.e.
rate of resistance. The position on the axis of abscissa is represented by
+1/2L on the right-hand side and -1/2L on the left-hand side.
According to the measurement results, the resistance of the transparent
conductive film of the present embodiment less varies at the end of the
bulb 1 at which it shows high antimony content and largely varies at the
central portion thereof at which it shows low antimony content. Such
variation of the resistance is caused during the production of the
fluorescent lamp, for example, by the oxidation of tin in the fluorescent
body sintering process and the reduction (deoxidation) of the tin oxide in
the gas-discharging process. Furthermore, during the lighting of the
fluorescent lamp, oxygen is removed from the tin oxide and tin remains,
thus increasing the conductivity.
The antimony has a property for stabilizing the conductivity, in the
fluorescent lamp according to this embodiment, the resistance of the
transparent conductive film less varies at the end portions of the bulb
and largely varies at the central portion thereof. Because of this reason,
the resistance distribution of the conductive film reaches an ideal
V-shape.
On the contrary, the resistance value of the transparent conductive film of
the fluorescent lamp of the conventional structure varies at every portion
of the bulb, and for this reason, the resistance distribution never
provide an ideal V-shape.
In comparison of a fluorescent lamp A having the resistance distribution of
the above (a) to (c) with a fluorescent lamp B of the resistance
distribution of the above (d) to (f) at a time when they were lightened,
the blackening phenomenon was visually observed after the lighting time of
about 1500 hours with respect to the lamp A but such blackening phenomenon
was visually observed after the lighting time of about 1000 hours with
respect to the lamp B.
As described hereinbefore with reference to FIG. 2, the transparent
conductive film having the above resistance distribution will be similarly
manufactured in the following manner with reference to FIGS. 7A and 7B.
As shown in FIG. 7A, a tubular glass bulb 1 opened at both ends is
prepared. The glass bulb 1 held at its horizontal position is put into a
heating oven and then only the end portions thereof are heated at a
temperature of about 580.degree. C. Under this state, mixed vapors of tin
tetrachloride and antimony trichloride are introduced into the glass bulb
1 from one end opening thereof and then discharged therefrom through the
other end opening. During this process, the dimethyltin dichloride and
antimony trichloride are put into contact with the heated glass bulb 1 and
then decomposed, oxidized and deposited in the form of tin oxide and
antimony oxide onto the inner surface of the bulb 1. The molar ratio of
the dimethyltin chloride to the antimony trichloride is approximately
99.3:0.7. The antimony content in the transparent conductive film 4 at the
end portion of the bulb 1 accords with this ratio because of high heating
temperature. At this time, the conductive film 4 is less formed at the
central portion of the glass bulb 1 because that portion is not heated.
Thereafter, as shown in FIG. 7B, while only the central portion of the bulb
1 is heated in the heating oven at a temperature of about 580.degree. C.,
the mixed vapors of tin tetrachloride and antimony trichloride are
introduced into the glass bulb 1 from one end opening thereof with a molar
ratio of, for example, about 99.5:0.5 to form a transparent conductive
film, including the antimony content of 0.5%, at the central portion of
the bulb 1.
According to the processes described above, the transparent conductive film
of the present embodiment can be formed in which the end portions of the
bulb has the antimony content of 1.5% and the central portion thereof has
the the antimony content of 0.5%. The fluorescent lamp having the
transparent conductive film manufactured of this process attains
substantially the same functions and effects as described above with
reference to FIG. 2.
Furthermore, according to a low-pressure mercury vapor discharge lamp of a
further embodiment, in which FIGS. 1 to 3 are commonly applied, in
comparison of the fluorescent lamp A' of the present invention having a
thin transparent conductive film with a fluorescent lamp B' of
conventional structure having a thick transparent conductive film having a
central portion of the thickness of about 120 nm, at a time when they were
lightened, the blackening phenomenon was visually observed after the
lighting time of about 1500 hours with respect to the lamp A' but such
blacking phenomenon was visually observed after the lighting time of about
1000 hours with respect to the lamp B'. Further, in comparison of the
starting voltage between these fluorescent lamps A' and B', there was
substantially no difference in the startability just after the production
thereof, but after the lighting time of about 1000 hours, the fluorescent
lamp A' of the present embodiment provided an excellent startability in
comparison with the fluorescent lamp B'.
The transparent conductive film 4 of the present embodiment contains
antimony of the concentration of 0.7 to 2.0 mol %, which is determined by
most suitable ranges of the degree of the resistance of the transparent
conductive film in the elapsed time due to antimony concentration, the
coloring degree (full-light transmittance) of the transparent conductive
film and the value of the resistance. This is of course mentioned to a
case of the transparent conductive film having a fine (microscopic)
structure including less residual of the undecomposed tin compound. This
will be explained hereunder with reference to FIG. 8.
FIG. 8 is a graph representing a relationship between the antimony
concentration and the relative resistance of the transparent conductive
film, in which the relative resistance is made to a value 1.0 at a time of
zero (0) antimony concentration. At this time, the relative resistance
decreases in accordance with the increasing of the antimony concentration
and then increases when the antimony concentration reaches 1.5 mol % being
the lowest value thereof.
FIG. 9 is a graph representing the degree of change of resistance in an
elapsed time, in which the resistance of the conductive film after the
lighting time of 100 hours is made to a value 1.0. At this time, the
resistance after the lighting time of about 1000 hours approaches the
value of 1.0 in accordance with the increasing of the antimony
concentration and the resistance does not substantially changes in the
case of the antimony concentration more than 0.7 mol %. In a case where
the transparent conductive film is not minutely formed, the resistance
varies largely and is not stabilized even in case of high antimony
concentration.
FIG. 10 is a graph representing the degree of coloring (full-light
transmittance) of the transparent conductive film 4, and as shown in FIG.
10, it gradually decreases in accordance with the increasing of the
antimony concentration. As most applicable ranges of these characteristic
values of the coloring degrees, ranges more than 0.7 mol % and less than
2.0 mol % will be selectively adapted. That is, in the cases of more than
0.7 mol % and less than 2.0 mol %, the resistance less varies in the
elapsed time and the transparent conductive film is less colored, thus
highly maintaining the light transmittance and being capable of making
thick the thickness of the conductive film for achieving a constant
conductivity with low resistance.
An experiment was performed for investigating the relationship between the
thickness of the transparent conductive film 4 and the blackening
generation rate after the lighting time of about 5000 hours. Such test
results are shown in FIG. 11, in which the coordinate axis represents the
ratio of the test lamps subjected to the causing of the blackening
phenomenon.
As shown in FIG. 11, the blackening generation ratio near the electrodes
varies at portions of the conductive film from electrodes, i.e. the ends
of the bulb, to portions of about 20 cm apart from the electrodes in
accordance with the thickness of the transparent conductive film. However,
the low blackening generation ratio is observed at portions apart,
inwardly of the bulb, from the 20 cm portions form the electrodes not
depending on the thickness of the transparent conductive film. According
to the above facts, it will be found that the blackening generation ratio
can be lowered at the portions of the bulb in the vicinity of the
electrodes by forming the transparent conductive film with thin thickness
at portions from the electrodes to the portions apart therefrom by for
example about 20 cm without the thickness of the central portion of the
bulb. It will be also observed that the blackening generation ratio is
also made relatively low with the thickness of less than 25 nm. In such
case, the condition of the conductive film is intentionally changed so as
not to change the resistance even when the thickness of the conductive
film differs.
FIG. 12 is a graph representing a relationship, obtained through
experiments, between the average film thickness of the transparent
conductive film at portions in the vicinity of the electrodes, i.e.
portions inwardly apart by about 20 cm from the electrodes, and the
blackening generation ratio at these portions after the lighting time of
about 5000 hours, and in this case, the resistance is made equal
throughout these portions. As can be seen from the characteristic features
of FIG. 12, the blackening generation ratio becomes smaller as the film
structure of the transparent conductive film is formed more thin and fine.
As described above, according to the fluorescent lamp of this embodiment,
the blacking generation ratio can be made small by forming the transparent
conductive film with thin thickness, and this thickness can be made small
by lowering the resistance by selecting the antimony concentration to a
range between 0.7 to 2.0 mol %, thus easily reducing the blackening
generation ratio. Furthermore, according to this embodiment, since the
resistance change of the transparent conductive film can be made small,
the generation of the blackening phenomenon can be suppressed or
controlled for a long time use. The antimony concentration within 0.7 to
2.0 mol % allows the transparent conductive film to maintain high light
transmittance.
In the embodiments described above, Xe gas may be utilized in substitution
for the mercury gas, and the Xe gas discharges a strong ultraviolet rays,
which largely varies the electric resistance of the transparent conductive
film. Accordingly, a microscopic discharge is caused at a portion near the
electrode, which may cause various adverse reactions to the phosphor film
and the glass bulb due to the microscopic discharge, which can be
suppressed by the present invention.
Furthermore, the transparent conductive film may be formed by other methods
such as spraying method.
Similar effects and advantages to those described above will be achieved
even if the resistance distribution of the transparent conductive film
does not provide an ideal V-shape.
According to the embodiments of the present invention described above, the
transparent conductive film having high ultraviolet ray decreasing
performance is formed to the portion at which the resistance thereof
likely varies, so that the resistance distribution is bilaterally
balanced, thus eliminating the generation of the blackening phenomenon
during the long time use of the discharge lamp with high quality.
Since tin oxide as the main component of the transparent conductive film
and antimony as the additive therefor are combined in use, thus realizing
the low-pressure mercury vapor discharge lamp of high reliability with
high quality.
The generation of the blackening phenomenon can be eliminated by making
thin the transparent conductive film thickness by specially defining the
content of the antimony to be added with high quality and high light
transmittance for a long time use of the lamp.
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